| Summary: | Studies were conducted using Scottish cashmere goats which were segregated into responsive and non-responsive individuals on the basis of ranked faecal egg count following artificial and natural gastrointestinal nematode infection. These studies demonstrate that caprine responsiveness is a relatively stable and heritable characteristic, largely unaffected by season and mode or site of infection. Initial comparative studies showed does to be considerably more susceptible to mixed artificial <I>teladorsagia circumcincta</I> and <I>Trichostrongylus vitrinus</I> infection than were ewes or worm-naive lambs. This was reflected in distinct differences in mucosal mast cell (MMC) and glouble leukocyte (GL) populations, the does having more GLs but many fewer MMCs than ewes. Theses differences together with the very low sheep mast cell proteinase concentrations recovered from doe tissue suggest that there are important functional differences in the mast cell responses of sheep and goats. The responses of breeding male and female goats were very consistent, with individuals occupying the same position of relative responsiveness while on pasture and after artificial challenge. Differences in the susceptibility of responders and non-responders were apparent in egg count following natural and artificial infection and selection was largely supported by worm burdens recovered after artificial challenge. There was a tendency for enhanced responsiveness to be associated with increased tissue eosinophil and GL numbers though this relationship wasn't very strong. However, responders were able to mount a more rapid and vigorous peripheral eosinophil response than were non-responders suggesting that peripheral eosinophil levels may be indicative of the ability of the host to respond to infection. Analysis of the cellular traffic of the gastric lymph showed that more resistant individuals were responding earlier. Results obtained from the first generation yearlings from the helminth-line showed that under the conditions encountered in these studies increased resistance to gastrointestinal nematode infection in Scottish cashmere goats is a heritable phenomenon with a heritabililty estimate (0.37) similar to those of production traits for which selection has been successful. Over the early stages of the programme selection for enhanced resistance appears to have had no detrimental effect upon productivity.
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